Introduction to Epidemiology of Influenza A (HINI) Infection

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Introduction to Epidemiology of Influenza A
(HINI) Infection

• Dr. Tong Ka Io
• Center for Disease Control Prevention
• 4th May, 2009

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Outline

• Situation update
• Characteristics of the disease
• Risk assessment
• Preventive measures

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Situation Update
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Influenza A (H1N1) human cases (2009.05.04)
Confirmed Deaths
Mexico 590 25
US 226 1
Canada 85

20 other countries 985 26
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Situation in Mexico

• Jan to Mar 11 all samples reconfirmed to be
  negative
• Mar 15/17 1st probable/confirmed case
• Apr 12 reported to WHO an ILI outbreak in a
  small community (Veracruz)
• Apr 17 Issued alert due to a case of atypical
  pneumonia (Oaxaca) and enhanced surveillance
• Apr 23 Canada HPA helped to confirm swine flu
  infection and reported to WHO
• Apr 27 School suspension in the whole country
• May 3 Epidemic easing

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Asia Pacific region

• Confirmed
• New Zealand...6
• Hong Kong1
• Korea1

• Suspected
• Australia
• Thailand
• Japan

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Characteristics of Disease
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Virology

• H1N1
• Same virus found in Mexico and US
• A new subtype not previously detected. A large
  part of the gene sequence is similar to that of
  the swine flu virus in US while a small part
  similar to that in Eurasia
• Resistant to amantadine and rimantidine but
  sensitive to oseltamivir (Tamiflu) and zanamivir
  (Relenza)

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Epidemiology
Mexico US
Temporal distribution 03.15 03.28
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Number of confirmed (N 97) and probable (N
260) cases of swine-origin influenza A (H1N1)
virus (S-OIV) infectionby date of illness
onsetMexico, March 15--April 26, 2009
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Confirmed human cases of swine-origin influenza A
(H1N1) infection with known dates of illness
onsetUnited States, March 28--April 27, 2009
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Epidemiology
Mexico US
Temporal distribution A double in the number of ILI cases over the country starting from the end of March All 32 states report suspected or probable cases Clusters of severe pneumonia cases and deaths in several administrative regions Cases first found in California and Texas that are adjacent to Mexico Cases are currently found in 30 states 63 in NY, 40 in Texas, 26 in California
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Epidemiology
Mexico US
Human distribution Confirmed cases are aged between 1-59. Fatal cases are mostly healthy people aged between 20 to 45 Fatal cases include healthcare workers and their families Confirmed cases are aged between 3-81, the median being 16. Non-healthcare workers, no contact history with pigs. The minority have travelled to Mexico but 85 are without travel history or contact history with confirmed cases.
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Number of patients and deaths from
laboratory-confirmed infection with swine-origin
influenza A (H1N1) virus (S-OIV) by age
groupMexico, April 1--27, 2009
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Places of transmission

• Families
• Medical establishments
• Schools

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Clinical manifestation

• Incubation undefined at present, estimated to be
  2-7 days by US. WHO adopts the longest incubation
  period of 14 days
• Manifestation
• US relatively mild self-limiting ILI. Vomiting
  and diarrhea are commonly seen
• Mexico Mild cases are common, mostly with
  symptoms of fever, cough, shortness of breath,
  vomiting, diarrhea. Severe cases have rapidly
  developed severe pneumonia and severe acute
  respiratory disease with high fatality
• Diagnosis RT-PCR on respiratory samples yields
  positive results for influenza A virus but unable
  to differentiate subtype

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Symptoms in an outbreak in a New York high school

• Cough...98
• Subjective fever...96
• Fatigue..89
• Headache..82
• Sore throat82
• Runny nose82
• Chills..80
• Myalgia..80

• Nausea55
• Abdominal pain50
• Diarrhea48
• Shortness of breath48
• Joint pain46

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Mexico official sources

• 25 among patients of ILI are suspected cases
• Among which, 10 are hospitalized for observation
• Among which, 1/3 are severe cases requiring an
  operation
• Fatality rate approximately 1.2

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Risk Assessment
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WHO assessment

• Event fulfils all 4 criteria for public health
  emergencies of international concern as defined
  in IHR (2005)
• Serious public health impact unusual or
  unexpected international spread significant
  risk of international travel or trade
  restrictions
• On April 25, on the advice of the Emergency
  Committee, WHO's Director-General announced that
  the situation constituted a public health
  emergency of international concern
• Recommending all countries to heighten
  surveillance for unusual outbreaks of ILI and
  pneumonia

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WHO assessment

• On April 27, WHO's Director-General raised the
  level of influenza pandemic alert from phase 3 to
  phase 4, stating
• Likelihood of a pandemic has increased but not
  inevitable
• Virus is capable of human-to-human transmission
  and community-level outbreaks.
• Given the widespread presence of the virus,
  containment of the outbreak is not feasible. The
  current focus should be on mitigation measures.

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WHO assessment

• On April 29, WHO's Director-General raised the
  level of influenza pandemic alert from phase 4 to
  5 , stating
• The pandemic is imminent
• All countries should immediately activate their
  pandemic preparedness plans
• At this stage, effective and essential measures
  include heightened surveillance, early detection
  and treatment of cases, and infection control in
  all health facilities

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WHO phases of pandemic alert -Phase 4

• Verified human-to-human transmission of an animal
  or human-animal influenza reassortant virus able
  to cause community-level outbreaks.
• The ability to cause sustained disease outbreaks
  in a community marks a significant upwards shift
  in the risk for a pandemic.
• Indicates a significant increase in risk of a
  pandemic but does not necessarily mean that a
  pandemic is a forgone conclusion.

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Phase 5

• Human-to-human spread of the virus into at least
  two countries in one WHO region. While most
  countries will not be affected at this stage
• Is a strong signal that a pandemic is imminent
  and that the time to finalize the organization,
  communication, and implementation of the planned
  mitigation measures is short.

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Phase 6 (pandemic phase)

• Community level outbreaks in at least one other
  country in a different WHO region in addition to
  the criteria defined in Phase 5.
• Indicate that a global pandemic is under way.

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Local assessment

• More serious than SARS outbreak in Feb 2003
• With both the characteristics of flu and SARS
• Conforming to initial characteristics of a
  pandemic

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Influenza A (H1N1) vs. SARS
SARS 2003.02 Influenza A (H1N1) 2009.04
Development 3 mths 1 mth
No. of suspected cases and deaths 305 infected 5 died gt2000 infected gt100 died
Scope of transmission Limited to Guangdong Spread to 3 continents and at least 8 countries
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With characteristics of flu

• Adapted for human transmission
• Rapid transmission
• Invisible transmission
• Enlarged through outbreaks in schools

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Outbreak in a New York high school

• Apr 23-24 222 sick students visited the school
  nursing office
• Apr 26 7 out of 9 samples tested positive for
  influenza A (H1N1)
• 44 preliminary confirmed cases
• Onset date Apr 20-24
• Aged between 14-21
• 68 non-Hispanic white, 16 Hispanic, 5
  non-Hispanic black, 11 of other races
• No travel history
• ILI symptoms. Only 1 has to be hospitalized for a
  short period
• Small number of students in the same school
  reported having travelled to Mexico

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Number of confirmed cases ( N 44) of
swine-origin influenza A (H1N1) virus infection
in a school, by date of illness onsetNew York
City, April 2009
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With characteristic of SARS

• Causes severe acute respiratory tract infection
• Super spreaders may exist
• Enlarged through outbreaks in medical
  establishments

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Clusters of severe pneumonia cases

• Cluster in San Luis Potosi involved 9 cases and 2
  persons died
• Cluster in Mexicali involved 3 cases and 2
  persons died
• Cluster in National Institute of Respiratory
  Diseases (INER) involved 6 cases and 2 persons
  died
• Dead cases were a doctor and his daughter. The
  other daughter of the doctor was hospitalized for
  pneumonia
• Rumour 2 interns died 6 days after being
  infected

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Conforming to initial characteristics of a
pandemic

• Current situation in Mexico does not conform to
  expectations for a pandemic
• Rapid international and inter-continental
  transmission
• Initial stage (1st wave) is usually less severe
• Severe cases and fatal cases are usually the
  young and prime aged

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Questions to be answered

• What is the real scope and transmission extent in
  Mexico?
• How many reported pneumonia cases are caused by
  Influenza A (H1N1)?
• Are these cases concentrated or widely dispersed?

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Questions to be answered

• Why cases in Mexico and US differ so much in the
  severity?
• Weakened virus?
• Super spreaders and outbreaks in medical
  settings?
• Lifestyles/hygiene practices?
• Level of medical services/vaccination?
• Genetic difference?

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Questions to be answered

• Can the seasonal influenza vaccine offer partial
  protection?
• According to US CDC, the seasonal influenza
  vaccine is unlikely to provide protection for
  Influenza A (H1N1)
• Obviously, cases in Mexico are more severe than
  those in US. Fatal cases are mostly the young and
  prime aged.

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Prognosis impossible outcomes

• A false alarm. Situation was being exaggerated
• Outbreaks controlled or eliminated via public
  health measures

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Prognosis possible outcomes

• Outbreaks stop by itself
• Transmission continued without touching off a
  pandemic, eventually becoming part of the
  seasonal influenza
• Resulting in a pandemic
• Serious impact during the first wave
• Serious impact only in the second wave

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2nd wave
1st wave
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Estimation for local region

• Although the origin of outbreak is distant from
  Macao and there are no direct flights between the
  two places, early cases may be imported at any
  time
• Once a pandemic has started, it will probably
  enter Macao within several weeks
• Since 2005, the Influenza Pandemic Preparedness
  Plan and preparation in Macao is maintained at a
  satisfactory level. It is believed that when
  Macao is attacked by the pandemic, the impact on
  health, society and economics can be reduced to a
  minimum

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Preventive Measures
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Vaccines

• Vaccination is the best method of prevention
• US CDC has begun to produce specific vaccines.
  However, mass production generally requires a
  period of 6 months

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1. Basic measures

• Keep contact with WHO, China MOH, health
  departments of neighboring regions so as to
  obtain the latest information
• Enhance risk communication and release timely
  information so as to inform all residents of the
  current situation and development, and adopt
  appropriate self-protection and personal hygiene
  measures
• Meet with the media regularly to report and
  explain the outbreak development
• CDC staff on duty and a 24-hr hotline in service
• Health education and promotion via the community
  network
• Health education and promotion by other
  government departments within their scope

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2. Deferment measures

• Issue travel alert and travel warning according
  to situation so that residents can take
  appropriate measures before, during and after
  their trip
• Strengthen temperature screening at all ports of
  entry, paying special attention to travellers
  from affected areas

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3. Early detection and isolation

• Heighten surveillance for ILI and outbreaks,
  virology of influenza, pneumonia of unknown
  causes
• Maintain close relationship and collaboration
  with WHO influenza laboratory network to increase
  the ability of virus testing
• Issue guidelines to public, private medical
  settings and healthcare workers so as to promptly
  detect and refer suspected cases
• Examine and repair isolation facilities and
  equipment so as to isolate suspected and
  confirmed cases when necessary

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4. Measures to prevent outbreaks in high-risk
institutions

• The Health Bureau coordinates all medical
  institutions to maintain good infection control
• With the help of DSEJ, coordinates all schools to
  perform preventive measures such as morning
  inspection, temperature measurement, school
  suspension for the sick, outbreak notification
  better and revise contingency plans so as to
  suspend school when necessary
• With the help of IAS, coordinates all nurseries
  to perform measures such as morning inspection,
  temperature measurement, school suspension for
  the sick coordinates all social facilities for
  outbreak notification, better and revise
  contingency plans so as to suspend social
  services when necessary

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5. Measures to respond to pandemic

• Health Bureau perfects and revises the Influenza
  Pandemic Preparedness Plan and substantial
  preparation so as to rapidly adjust functions,
  allocate resources, raise capacity and rescue
  patients in times of a pandemic
• All relevant departments perfect and revise
  preparedness plans and substantial preparation so
  as to maintain basic social functions and
  services in times of a pandemic

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6. Restorative measures

• All relevant departments perfect and revise
  post-pandemic restorative plans and preparation
  for social, economic, psychological aspects so as
  to achieve fast recovery of the community after
  the pandemic.

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